It is very important that you order the wider size kit for the job so you can trim off excess. Make sure that you calculate the width as the length of the two sides and the bottom. Similarly the length must allow for stop-ends, there is usually at least one, add 200mm for each stop-end. Then pick the required kit from the part number table.

Example: A leaking 400mm box gutter is 28.6 meters long with 110mm sides and has an end stop at both ends of the building. Which kit is required? . . . Using the diagram below we calculate the width as 620mm and the length as 29m.

Answer: We choose the 600mm by 50m kit which is kit number 3600-050. We can allow the sides to run 10mm short along the sides (only at the outlet end) , you have to get the 50m kit so that there are no joins in liner